One has to ask why has the fuse on the shower gone as this is not normal and maybe not a minor repair? Electric showers can be dangerous things - get it checked out by a qualified electrician. Better safe than sorry on this one
Does tenant know where the fuse board is and why should she necessarily know what to look for? She is renting a property and she expects it all to work - sounds reasonable to me.
The tenant rented property with shower and that is what you have to provide - what she saw at the viewing and what she is paying her rent for.
Freedom at the point of zero............